Where is it that you're trying to connect to?
The only time I can see that message coming up is if you tried to connect to a private server or network and you don't have authorization to be on that server/network.
There are hundreds (or possibly) thousands of public accessable (sp?) networks out there, and a fair number of them are listed in the servers.ini file which comes with mIRC.
If you're getting that message and you're trying to connect to one of the networks that is in the mIRC servers.ini file, then I suggest you download a fresh copy of the servers.ini file from the mIRC website and replace your current version with the one you downloaded.
If you're trying to connect to a private network, then you have to have authorization and there's nothing more anyone here can do to help.
Please note (just thought of this) that you might get that (or similar) if you tried to connect to an irc network from your workplace or school and the workplace/school doesn't permit IRC access via their network(s).
